The dashboard and center console do not need to be comprehensively disassembled like this to remove the transmission. It was apart for other reasons. But the picture is important to note the shape and size of the hole in the floor.
The lower shift boot was a pain to put back into place. Fortunately it does not need to be removed when pulling the trans, the shift lever can be removed with the lower boot in place.
The '80 (SA) transmission is on the left, the '85 (FB) is on the right. The FB trans is slightly more forward, but you can still see how much further forward the SA shifter is. It would come up roughly where the dashboard's crossbar is, and that crossbar is metal. You'd have to cut that, lose the ashtray, cut through double-thickness floorpan, and find some way of adequately covering the gaping new holes in the floor and dashboard. I was intending to try to put the SA trans in as-is but laying them side by side made me change my mind. (The window switches and joystick could have gone where the current shifter sprouted up and I could have lost the center console, though)
I tried for 20 minutes with various special tools trying to get the clutch slave off, so I just undid the line and left it attached to the transmission. This isn't a problem if you do not have the beehive oil heater.
The clutches to the right are why the trans came out in the first place. The old was a cheapo remanufactured unit, and the rivets on the pressure plate were preventing full engagement. Disc was all burnt to hell from slippage. The scary-loud bearing whine (155k miles) was why I wanted to put in the no-noise, excellent shifting, 142k mile SA trans.
A nice shot of the differences in towers. The FB shifter is remotely mounted, positioned directly over the end of the transmission, has its own separate lubricant (there is an O-ring between tower and transmission to prevent lube from draining out and leaving it dry) and the locator pin is in the front.
The SA shifter is right there roughly between the end of the transmission and the transmission mount, shares lubricant with the transmission from splash and slosh, and the locator pin is towards the rear of the car.
You can fill a transmission with the SA setup through the shifter hole. You can't do that with an FB shift tower because of the O-ring.
SA transmission tailshaft removal: Remove shift tower, flip the shifter block to the side (starter side of transmission) so that the rod disengages the shift fingers. With the trans on end like this, it'll just thunk downwards when disengaged and will feel like it's not connected to anything. Then get to work removing all of the transmission through-bolts.
The shift rod will stay attached to the tailhousing. It won't be used anyway.
We took a lot of pictures of the disassembly of the FB setup, but this is all you really need to see, and this is a bandwidth-limited site. Remove the side cover of the tower, remove the bolt holding the shift block to the shift rod, slide the block up on the rod and hold it up through the shifter hole with one hand, and use pliers in the other hand to rotate the shift rod just like in the SA trans, towards the starter side until it drops free.
You can't turn the shaft far enough with the block in place so it has to get unbolted. Once the shaft drops, the block won't stay in there on its own, so it has to be one of the small parts in the parts pile instead of staying as part of a larger, harder-to-lose assembly.
FB transmission, tailshaft removed. The shift rod has a finger on the end that rides in these slots in the shift fingers. The shortest one is 1-2, middle is 3-4, long is 5-R. Note that the angle of the slot is pointing towards the transmission's mainshaft. Also note that the fingers are held on to their respective shift rods with roll pins.
SA tranny, tailshaft removed. Note that the angle described by the shift fingers' slots is much different. If you put a straightedge in the slot, it would point roughly straight down to the ground, if the trans was in the car. The main shift rod is in a different place in the SA tailhousing versus the FB. The shift fingers need to be changed over with the tailhousing.
Also carefully note that the fingers are also held on to their shafts with roll pins. Most SA transmissions have capscrews (bolts) holding the fingers to the shafts. You cannot put FB fingers on these because the roll pins would rattle around in the larger-diameter threaded holes. Only SA's with VINs later than SA22C-606775 will have come with a rollpin-type transmission from the factory. My '80 was SA22C-608250, and was born in May, 1980. (Some things you just never forget)
If you really, really wanted to, you probably could swap an FB tailhousing onto a pre-606775 transmission if you disassembled further and changed the shift rods, and possibly shift forks, along with the fingers. I cannot say that for certain, but hell, the shifter relocation has been the only major change to the transmission in the 25-30 years they have been making it. Yep, an '04 5-speed Miata is using the same basic transmission as in a '78 RX-7, and most internal parts will interchange too.
Both transmissions in same shot for comparison. There are three things to note. First, the relative cleanliness of the transmissions. You could practically EAT out of the inside of the SA unit, while the FB's internals are coated with horrible sludge. I'd put two quarts of ATF into the FB trans two days earlier (it was a heavy leaker due to a clogged vent, and Redline MTL seems to just be expensive synthetic ATF. They both work as well.) and it came out black with silvery streaks. The '80 transmission had its fluid changed twice in its life that I can recall, once at 89k when I put a new clutch in and once at 119k when I put the ported engine in.
Second, look at the gears. What you can see is 5th gear, 5th and Reverse are on the end of the stack. The SA transmission has huge, mongo gear teeth, whereas the '85 trans has these little Swiss-watch looking teeth. The changeover to fine-pitch teeth was in '82 or '83. Coarser teeth are more tolerant of bearing and case flex, whereas finer teeth are not. These transmissions will flex a lot under heavy load due to the design, especially in 2nd and 3rd because they are in the middle of a long span between bearings, 3rd moreso than 2nd because of any tolerance/give in the input shaft-to-mainshaft bearing. 4th isn't a gear, it just directly drives the mainshaft from the input shaft, and the end of the mainshaft just rides in the input shaft on a little needle bearing similar in size to the pilot bearing, only it sees a LOT of side loading.
I have never heard of a coarse-geared trans eating gears, but go and ask GSL-SE, FC, or Miata people with goodly power and/or strong clutches how often they strip third gear.
Third, note that the '85 trans countershaft's end bearing/5th/Reverse are held on with a staked locknut, while the SA trans just uses a circlip. I don't know when that redesign was made, but it's overkill. The circlip never sees load except when coasting in 5th (acceleration puts a side load in the other direction, and Reverse is straight-cut) and you are simply *not* going to have any kind of major reverse load in 5th, unless maybe you're coasting at 75 with a siezed engine and you pop the clutch. In which case, you'd deserve to have the trans self-disassemble anyway...
It's a mutant! FB fingers on SA trans.
When knocking the roll pins out, use a punch that is large enough to not fall into the center of the roll pin. Also, just knock the pins out enough to clear the shift rod, makes it SO much easier to knock them back in place when putting the fingers on.
The brown stuff is Permatex Aviation Sealer. Loctite 515 was what I'm used to using for putting transmissions back together, but I had the Aviation Sealer lying around, and it has that noxious odor that reminds me that yes, it really is going back together again.
Reassembly is just the reverse of disassembly, except it generally goes faster. Less FUD (Fear, Uncertainty, Doubt) slowing the process.
It shifts!
Side plate is not on yet. That also got a cleaning and some Aviation Sealer before getting popped back on.
I neglected to change the speedometer drive gear (worm gear on mainshaft) over to the '85 unit. '79-83 transmissions had a different tooth pitch according to SoloMiata's Mazda drivetrain page, but I didn't check. Of course, I remember this *after* torquing all of the case bolts. Instead of pulling it all back apart, I just swapped the driven gear/housing over. Just one bolt.
I neglected to check for a difference in driven gear, too. *sheepish grin* Either the '80 combo or the '85 combo will work, all 12A RX-7s except early '84 had the same 3.91 gearing and tire size, and the early '84 was so close that it was effectively the same anyway. (Mazda playing with tooth pitch again, probably)
The SA fingers and tailhousing went onto the FB trans and it was bolted back together. Again, much nicer to deal with assemblies instead of a pile of parts.
The new clutch (Series 4 N/A, used. Why? It was free, and the clutch from the '83 engine in the SA was ready to frag from dragstrip abuse) went in, followed by the SA/FB transmission. The slightly shorter 5th gear is noticably better on the highway. Then a couple weeks later, on the way home from a drag strip where they did not permit wet burnouts (still managed 16.40 at 83.5 with traction issues, not bad for loaded and 95% stock), I was exiting a rest area and the clutch pedal stayed glued to the floor, clutch still engaged, during a 1-2 shift. No 2 weeks notice, no 5 minute warning, something in the clutch decided it was fed up and walked off the job right then and there. It definitely wasn't a hydraulic issue since, once the pedal was pulled up manually, depressing it with the engine running felt like badly pulsating brakes. Not a fun thing to have happen to you when it's dark, raining, about 30 miles from home, and you have to drive home in 4th gear (because shifting to 5th sans clutch is too difficult) with an as-yes-undiagnosed clutch problem, and God-knows-how-much rotational mass aiming its partially broken inertia right at your feet.
Next day, trans out again, turned out a quarter of the pressure plate side lining broke apart and wedged itself between the disc and the pressure plate. So "White Trash"'s visibly-ready-to-come-apart disk had to go in the next day, and the car hasn't seen the drag strip since, since I'm fresh out of 225mm clutch disks.
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created November 03, 2003
Pete Remner aka peejay or sometimes SPRT